Determination of moisture in fertilisers and materials insoluble in methanol

The moisture content of a fertiliser as manufactured has a significant effect on its tendency to cake during storage. The lower the moisture content the better, but on the other hand any unnecessary drying leads to extra costs in manufacture, and therefore a rapid, reliable and accurate method for the determination of moisture is necessary. Of those available, titration with Fischer reagent is of the most general application; oven drying, for example, cannot be used with fertilisers containing ammonium nitrate. To ensure complete reaction with the reagent the fertiliser must be finely ground and it is, of course, essential that the grinding be carried out with neither loss nor gain of moisture. An apparatus has been designed and constructed that enables grinding of the fertiliser and titration of the moisture to be completed in a single vessel. Grinding is effected under methanol by a high-speed cutter and the Fischer reagent is then added automatically, the end-point being detected by a sensing electrode. Electronic valves were used in the original apparatus, but a transistorised version has now been made, which is compact and more convenient for laboratory use. Although designed primarily for the examination of fertilisers the apparatus can be used for determining moisture in any solid that is insoluble in methanol; it has been found useful for determining trace amounts of water in oils. The method and the apparatus are the subject of U.K. Patent No. 1,021, 745 granted to Imperial Chemical Industries Limited.